opcua-proxy

README

OPC-UA proxy

A proxy microservice connecting to an OPC-UA server and offering:

• Data change subscriptions through Centrifugo.
• Nodes values in JSON format.

Specifications

Nodes object

OPC-UA nodes are represented as a JSON object with following fields:

• namespaceURI: namespace URI for nodes to monitor (string)
• nodes: array of node identifiers, with mapping below:

JSON type	NodeID type
Integer (positive whole number)	Numeric
String	String

Centrifugo subscriptions

• A Centrifugo server (at least v3.1.1) is configured to proxy subscriptions to this service (/centrifugo/subscribe endpoint).
• Clients interested in OPC-UA values changes subscribe to Centrifugo with following characteristics:
  • Channel: name and interval, separated by @, e.g. my_nodes@2000, with:
    • name: unique identifier for each nodes set.
    • interval: publishing interval in milliseconds.
    • Note: channel namespace is reserved for configuring the proxy endpoint.
  • Data: Nodes object (see above).

Nodes values endpoint

A GET request on /values endpoint returns the configured nodes data values, in JSON format. Request URL parameters are expected to each have one value and will end up in the tags property of JSON output.

The nodes to be read are defined in a JSON file, located in configured path, and containing an array of Nodes objects (see above).

Data flow

Connection to OPC-UA server and session establishment are considered to have been done successfully.

Subscriptions

sequenceDiagram
    participant Client
    participant Centrifugo as Centrifugo server
    participant Proxy as Centrifugo / OPC-UA<br>proxy
    participant OPCServer as OPC-UA server
    alt unrecognized channel
        Client->>+Centrifugo: Subscribes to a channel
        Centrifugo->>+Proxy: Proxies the subscription request
        Proxy-->>-Centrifugo: Subscription allowed
        Centrifugo-->>-Client: Success
    else Heartbeat channel
        Client->>+Centrifugo: Subscribes to heartbeat channel
        Centrifugo->>+Proxy: Proxies the subscription request
        Proxy-->>-Centrifugo: Subscription allowed
        Centrifugo-->>-Client: Success
        loop Each heartbeat interval
            Proxy-)Centrifugo: Publishes status
            Centrifugo-)Client: Notifies status
        end
    else OPC-UA related channel
        Client->>+Centrifugo: Subscribes to a channel
        Centrifugo->>+Proxy: Proxies the subscription request
        opt No subscription for this refresh interval
            Proxy->>+OPCServer: Create subscription
            OPCServer-->>-Proxy: Subscription created
        end
        Proxy->>+OPCServer: Create monitored item
        OPCServer-->>-Proxy: Monitored item created
        Proxy-->>-Centrifugo: Subscription allowed
        Centrifugo-->>-Client: Success
        loop Each publishing interval with data change
            OPCServer-)Proxy: Data change notification
            activate Proxy
            Proxy-)Centrifugo: Publish
            deactivate Proxy
            activate Centrifugo
            Centrifugo-)Client: Notifies data change
            deactivate Centrifugo
        end
    end

Nodes values

sequenceDiagram
    participant Client
    participant Proxy as Centrifugo / OPC-UA<br>proxy
    participant OPCServer as OPC-UA server
    Client->>+Proxy: Requests nodes values
    Proxy->>+OPCServer: Reads nodes data values
    OPCServer-->>-Proxy: Sends data values
    Proxy-->>-Client: Sends values in JSON format

Configuration

This project uses standard library's flag and https://github.com/peterbourgon/ff packages, configuration can be provided by flags or environment variables.

$ opcua-proxy -help
USAGE
  opcua-proxy [options]

OPTIONS
  Flag                     Env Var                 Description
  -centrifugo-api-address  CENTRIFUGO_API_ADDRESS  Centrifugo API endpoint
  -centrifugo-api-key      CENTRIFUGO_API_KEY      Centrifugo API key
  -centrifugo-namespace    CENTRIFUGO_NAMESPACE    Centrifugo channel namespace for this instance
  -debug                                           log debug information (default: false)
  -heartbeat-interval      HEARTBEAT_INTERVAL      Heartbeat interval (default: 5s)
  -opcua-cert-file         OPCUA_CERT_FILE         certificate file path for OPC-UA secure channel (optional)
  -opcua-key-file          OPCUA_KEY_FILE          private key file path for OPC-UA secure channel (optional)
  -opcua-password          OPCUA_PASSWORD          password for OPC-UA authentication (optional)
  -opcua-server-url        OPCUA_SERVER_URL        OPC-UA server endpoint URL (default: opc.tcp://127.0.0.1:4840)
  -opcua-tidy-interval     OPCUA_TIDY_INTERVAL     interval at which to tidy-up OPC-UA subscriptions (default: 30s)
  -opcua-user              OPCUA_USER              user name for OPC-UA authentication (optional)
  -proxy-listen            PROXY_LISTEN            Centrifugo proxy listen address (default: :8080)
  -read-nodes-url          READ_NODES_URL          URL to query for nodes to read